It is known that heat-sealing thermoplastic adhesives based in particular on copolyamides, copolyesters or polyurethanes can be used for bonding purposes, more especially for bonding textile substrates (front fixing). These adhesives have to be processible at temperatures of from about 100.degree. to 170.degree. C and are required to develop strong adhesion with respect to any type of substrate to be bonded, more especially textile substrates. The adhesion which they develop is required to remain substantially intact under the stresses of, for example, washing and dry cleaning. Outstanding significance in this field has been acquired by copolyamides containing from 80 to 20% by weight of the basic unit, lauric lactam, and correspondingly from 20 to 80% by weight of the basic unit of one or more other polyamide-forming materials as described in German Auslegeschrift No. 1,253,449. Copolyamides which can be processed at particularly low temperatures contain from 25 to 35% by weight of caprolactam, from 20 to 40% by weight of lauric lactam, from 8 to 25% by weight of hexamethylene diamine adipate and from 10 to 40% by weight of the hexamethylene diamine salt of the acid of formula I EQU hooc--(ch.sub.2).sub.n --COOH I
in which n = 7, 8, 10 or 11 (as described in German Offenlegungsschrift No. 2,324,159), or 30% by weight of caprolactam, from 30 to 35% by weight of lauric lactam, from 10 to 15% by weight of hexamethylene diamine adipate or from 15 to 35% by weight of the hexamethylene diamine salt of the acid of formula I (as described in German Offenlegungsschrift No. 2,324,159) in co-polymerised form as basic units. Copolyesters and polyurethanes are also known as thermoplastic adhesives (as described in U.S. Pat. No. 3,669,921 and German Offenlegungsschrift No. 1,930,340 and 1,769,482).
Known thermoplastic adhesives based on copolyamide, copolyesters and polyurethane, in particular those based on copolyamide, develop satisfactory adhesion with respect to numerous interlining and outer fabrics of the type used in the clothing industry and retain this adhesion without significant losses even after washing or after dry cleaning. It is this factor which is responsible for the hitherto unexpected use of, in particular, copolyamides for front fixing. However, the level of adhesion developed by thermoplastic adhesives based on the polymers described above with respect to outer fabrics which are hydrophobically finished with silicone compounds, for example raincoat fabrics of polyester or polyester-cotton mixtures, are far from satisfactory, especially after dry cleaning, so that these polymers are unsuitable for this purpose.
An object of this invention is to provide a heat-sealing thermoplastic adhesive which is suitable for the heat-sealing of substrates which have been hydrophobically treated, more especially with silicone compounds.